The importance of proteolytic activity within the central nervous system (CNS) in both normal and pathological processes is well established. However, the mechanisms whereby proteinase activity contributes to such complex processes as axonal extension, synaptic remodeling or neuronal survival are not known. Many different proteinases and their inhibitors are known to be expressed in both the developing and the adult CNS. These include members of the serine proteinase family and their inhibitors. This application examines the biology of one recently identified serine proteinase inhibitors, neuroserpin. Neuroserpin is a member of serpin gene family of serine proteinase inhibitors, and inactivates the serine proteinase tissue-type plasminogen activator (tPA). TPA has been implicated in processes that promote neuronal cell death, and is also thought to be involved in events that require neuronal plasticity such as axonal extension, synaptic remodeling, long-term potentiation, kindling and seizure. Accordingly, this proposal will focus on understanding the basic biology of neuroserpin and on its role in promoting neuronal cell survival. By using a combination of biochemical, molecular and genetic approaches both in vitro and in vivo, and building on previous studies of neuroserpin, a number of important interactions will be characterized. We will test the hypotheses that: (1) neuroserpin is expressed in neurons and targeted to a regulated secretion pathway where it is likely to be released at the synapse; (2) in vivo, neuroserpin's primary function is to regulate tPA activity; and (3) neuroserpin is a potent neuroprotectant increasing neuronal survival after insults such as stroke or seizure. Sensitive assays will be developed to localize neuroserpin and tPA within the cell and to characterize their trafficking. Finally, animal models will be used to examine the role of neuroserpin and tPA in pathologies associated with both stroke and seizure, and the potential therapeutic benefit of neuroserpin administration will be tested.